Monitoring Land Use and Land Cover Effects on Water Quality in Cheung Ek Lake using ASTER Images

Abstract

Cheung Ek Lake is the biggest natural treatment plant for nearly 80% of wastewater and storm-water from Phnom Penh city. Land Use and Land Cover (LULC) changes of the lake and its catchment area could deteriorate capacity of the lake in purifying wastewater and affect to its water quality. The study aims to assess the relationship between LULC changes and water quality using ASTER images with field observations. Three pairs of temporal ASTER images in 2002, 2009 and 2011 acquired in dry season were used to make LULC map with five classes: (1) Urban or built-up areas, (2) rangeland, (3) agricultural land, (4) water bodies and (5) barren land, using Maximum Likelihood (ML) classification method. Post-classification comparison was chosen to study changes from 2002 to 2009 and from 2009 to 2011. The water quality data of the Ministry of Environment from 2000 to 2013 were used to study water quality change. Spatial distribution of water quality parameters including total phosphorus, total nitrogen, chemical oxygen demand, five-day biochemical oxygen demand, total suspended solids and chlorophyll-a was observed in the rainy and dry seasons in 2012 and 2013, respectively. The results showed that ML gave moderate level with overall accuracy of around 60% and Kappa coefficient of around 0.48 for classification images in all three dates. Also, some significant change were happened between 2002 and 2011; rangeland decreased by approximately 22%, while agricultural land and urban or built-up areas increased by more than 2 and 16%, respectively. In addition to the downward trend of water quality status changes recorded by the Ministry of Environment from 2000 to 2013, the spatial distribution maps revealed that wastewater from the city was the main source of water quality deterioration. These results might be suggested that LULC changes of the lake’s catchment area appeared to have negative effects on water quality of the lake.